I searched a lot but could not find a duplicating issue. So I created a new one.

Background

In 1.12 and earlier versions, it was "harder" to swim up a water stream that was flowing down. It took longer than a stream of source blocks. Downward speed was also faster in falling water.

The bug

In 1.13, now the player sink/swim up speed in downward flowing water is the same as in source blocks. The falling property of the water has no effect. This also affects mobs.